1、Immune SystemGuarding against diseaseThe not-so-common cold A“cold”is an infection of the mucus membranes of the respiratory tract by a rhinovirus.Over 100 rhinoviruses have been identified,which is one reason why we dont become immune to“the cold.”Cold mythsColds and“the flu”are different illnesses
2、.Not every respiratory infection is“the flu.”Colds are not caused by getting chilled.This belief comes from medical ideas of prior centuries,when it was believed that illness was caused by an imbalance of“humors,”and that a person with a cold actually had too much“coldness.”“Feed a cold,starve a fev
3、er”also comes from prior centuries,when it was thought that people with a cold had too much“cold”and“moisture”in their bodies,and needed food to increase heat,while people with fever had too much“dryness”and“heat,”so needed less food to cool them down.Cold vs.“Flu”(influenza)SymptomsColdFluFeverrare
4、characteristicHeadachemild(sinus)strongAches&Painsslightusual,strongFatiguemild2-3 weeksExhaustionneverearly,profoundStuffy noseusualsometimesSneezingusualsometimesSore throatcommonsometimesChest discomfortmildcommon,strongVirus vs.Bacteria Colds are caused by a virus,which is a non-living particle
5、that contains genetic material,and hijacks your cells to reproduce.Bacteria are living organisms that can reproduce on their own.First line of defense Non-specific defenses are designed to prevent infections by viruses and bacteria.These include:Intact skin Mucus and Cilia PhagocytesRole of skin Dea
6、d skin cells are constantly sloughed off,making it hard for invaders to colonize.Sweat and oils contain anti-microbial chemicals,including some antibiotics.Role of mucus and cilia Mucus contains lysozymes,enzymes that destroy bacterial cell walls.The normal flow of mucus washes bacteria and viruses
7、off of mucus membranes.Cilia in the respiratory tract move mucus out of the lungs to keep bacteria and viruses out.Role of phagocytes Phagocytes are several types of white blood cells(including macrophages and neutrophils)that seek and destroy invaders.Some also destroy damaged body cells.Phagocytes
8、 are attracted by an inflammatory response of damaged cells.Role of inflammation Inflammation is signaled by mast cells,which release histamine.Histamine causes fluids to collect around an injury to dilute toxins.This causes swelling.The temperature of the tissues may rise,which can kill temperature
9、-sensitive microbes.Role of fever Fever is a defense mechanism that can destroy many types of microbes.Fever also helps fight viral infections by increasing interferon production.While high fevers can be dangerous,some doctors recommend letting low fevers run their course without taking aspirin or i
10、buprofen.Ouch!Specific defenses Specific defenses are those that give us immunity to certain diseases.In specific defenses,the immune system forms a chemical“memory”of the invading microbe.If the microbe is encountered again,the body reacts so quickly that few or no symptoms are felt.Major players T
11、he major players in the immune system include:Macrophage T cells(helper,cytotoxic,memory)B cells(plasma,memory)AntibodiesSome vocabulary:Antibody:a protein produced by the human immune system to tag and destroy invasive microbes.Antibiotic:various chemicals produced by certain soil microbes that are
12、 toxic to many bacteria.Some we use as medicines.Antigen:any protein that our immune system recognizes as“not self.”Antibodies Antibodies are assembled out of protein chains.There are many different chains that the immune system assembles in different ways to make different antibodies.Antigen recogn
13、ition Cells of the immune system are“trained”to recognize“self”proteins vs.“not self”proteins.If an antigen(“not self”)protein is encountered by a macrophage,it will bring the protein to a helper T-cell for identification.If the helper T-cell recognizes the protein as“not self,”it will launch an imm
14、une response.Helper T cells Helper T-cells have receptors for recognizing antigens.If they are presented with an antigen,they release cytokines to stimulate B-cell division.The helper T-cell is the key cell to signal an immune response.If helper T-cells are disabled,as they are in people with AIDS,t
15、he immune system will not respond.B cells B-cells in general produce antibodies.Those with antibodies that bind with the invaders antigen are stimulated to reproduce rapidly.B-cells differentiate into either plasma cells or memory B-cells.Plasma cells rapidly produce antibodies.Memory cells retain t
16、he“memory”of the invader and remain ready to divide rapidly if an invasion occurs again.Clonal SelectionRole of antibodies Antibodies released into the blood stream will bind to the antigens that they are specific for.Antibodies may disable some microbes,or cause them to stick together(agglutinate).
17、They“tag”microbes so that the microbes are quickly recognized by various white blood cells.“Killer”T cells While B-cells divide and differentiate,so do T-cells.Some T-cells become cytotoxic,or“killer”T-cells.These T-cells seek out and destroy any antigens in the system,and destroy microbes“tagged”by
18、 antibodies.Some cytotoxic T-cells can recognize and destroy cancer cells.Calling a halt When the invader is destroyed,the helper T-cell calls a halt to the immune response.Memory T-cells are formed,which can quickly divide and produce cytotoxic T-cells to quickly fight off the invader if it is enco
19、untered again in the future.Helping the immune system Medical science has created to systems for augmenting the human immune system:Antibiotics VaccinesHow antibiotics work Antibiotics help destroy bacteria(but not viruses).Antibiotics work in one of several ways:Slowing bacteria reproduction.Interf
20、ering with bacterial cell wall formation.Antibiotic myths Antibiotics are not antibodies.Antibiotics do not weaken our immune system.They help it by weakening bacteria.Humans do not become“immune”to antibiotics.Bacteria that resist antibiotics and are not completely destroyed may multiply,producing
21、more antibiotic-resistant bacteria.Vaccine history Variolation:The deliberate inoculation of people with secretions from smallpox(Variola)sores.Used for centuries in Asia and Africa.Vaccination:Invented by Edward Jenner in 1796.Jenner knew that dairy maids who had contracted cowpox never got smallpo
22、x.He inoculated a boy with secretions from cowpox sores,and showed the boy was immune to smallpox.(From vacca,Latin for cow.)How vaccines work Modern vaccines are created from killed bacteria or viruses,or fragments of proteins from these microbes.The proteins are recognized as antigens by our immun
23、e systems.This causes a mild immune response.Memory T-cells and B-cells remain ready to fight off the illness if it is encountered again.Vaccine myths The flu vaccine does not give you the flu.Some people get the vaccine too late,or catch a cold and think they have the flu.Vaccines are not less effe
24、ctive than a“natural”infection with the illness.The immunity is the same,and a mild response to a vaccine is much less risky than a full-blown infection of measles.The proposed link between vaccines and autism turns out to have been greatly exaggerated.But I caught a cold.again!Because there are ove
25、r 100 different known rhinoviruses,its possible to catch colds again and again.In addition,cold viruses can mutate quickly.No sooner do we have immunity to one form than along comes another.Echinacea?Echinacea is supposed to“strengthen”the immune system.Studies in petrie dishes showed Echinacea stim
26、ulated white blood cells to produce more virus-killing peroxides,but controlled human trials have found no significant effects.Evolution of the flu Flu viruses also mutate quickly.The same form of the flu may have the ability to infect several different vertebrate animals.Different forms may hybridi
27、ze their genetic material,causing new strains to develop in a single generation.New FluAllergies Allergies are an immune system reaction to harmless antigens.Some,such as pollen,may get in through the respiratory system.Fragments of food proteins may get through the digestive system.The next time th
28、ese proteins are encountered,the immune system attacks them.Achoo!Pollen is a harmless protein,yet we can become allergic to it.Most of the symptoms are caused by histamines released by mast cells.That is why antihistamines are used to treat allergies.Autoimmune disorders Autoimmune disorders occur
29、when the immune system fails to recognize a protein as“self”and launches an attack.Multiple sclerosis,lupus,and rheumatoid arthritis are examples.None of these can be cured,but they can be controlled with drugs.Cancer Cancer occurs when the mechanisms that control cell division fail,and body cells d
30、ivide out of control.Cytotoxic T-cells can recognize and destroy these cells.But if division is too rapid,the T-cells cannot keep up.Some cancer research involves assisting cytotoxic T-cells in recognizing and destroying cancer cells.SCID Severe Combined Immune Deficiency is a genetic condition in w
31、hich one or more genes for proteins crucial for the immune system are defective.Children born with SCID have no immune system.Gene therapy has been used to inject a good copy of the defective gene into blood cells or bone marrow cells.In several cases this has been effective,though it is still exper
32、imental.AIDS AIDS(Acquired Immune Deficiency Syndrome)is caused by an infection by the HIV(Human Immunodeficiency Virus),which attacks and destroys T-helper cells.Because it attacks the immune system directly,finding a vaccine has been difficult.Some drugs can slow down HIV reproduction,but no cure exists yet.Prevention is still the best“cure.”
